Super-Schottky diodes and Josephson devices are electronic devices whose current-voltage response is highly non-linear. These have been used as radiation detectors and mixers for operation in the microwave, millimeter and higher frequency range. The conversion efficiency of these mixers is related to the degree of non-linearity of the current-voltage response. This non-linearity occurs over a small voltage range and becomes greater as the temperature becomes lower. The higher the non-linearity is, the higher is the efficiency of the mixer. Typically these devices must be cooled to liquid helium temperatures to improve their efficiency.